1. Field of the Invention
The present invention relates to an apparatus, installed on a vehicle disk wheel manufacturing line, for truing roundness of an annular rim element of a disk wheel. More particularly, the invention relates to an apparatus for truing the rim element such that rim bead seat portions located at axially end portions of the rim element are in alignment with each other and the rim element has no local, radially inwardly deformed portion over its entire circumference.
2. Description of Related Art
A vehicle disk wheel is manufactured in the following way. Firstly, a coiled plate having a predetermined width is developed and is successively cut at a predetermined length to provide flat plates. Each flat plate is conveyed to a coiler which rounds the flat plate. The rounded plate is conveyed to a flush-butt welding station, where both ends of the rounded plate are butt-welded together to provide an annular element. Then, the annular element is conveyed to a flaring station, where axially end portions of the annular element are flared. The flared annular element is then conveyed to a rim contour forming station having a plurality of roll-forming machines arranged in series along the line, where the flared annular element is roll-formed to a rim element having a rough rim contour. The rim element is then conveyed to a shaping apparatus, where the rim element is trued in its roundness by the shaping apparatus. Such a shaping apparatus is often called an expander that usually has a die circumferentially split into a plurality of die elements. The die elements are inserted into the rim element and are spread in the radial direction of the die to radially expand the rim element from the inside thereof. Through the expansion, the shaping apparatus trues the roundness of the rim element. Then, the shaped rim element is conveyed to a disk insertion station, where a disk is inserted into the rim element. Then, the assembly of the rim element and the disk is conveyed to a welding station, where the rim element and the disk are spot-welded together to provide a disk wheel. Finally, the disk wheel is conveyed to a coating station, where the disk wheel is coated.
FIG. 4 illustrates a prior art shaping apparatus and a rim element 62 to be trued in roundness. As is well known, rim element 62 includes a flange portion 62a, a rim bead seat portion 62b, and a drop portion 62c. Rim element 62 is shaped, by a first die circumferentially split into a plurality of first die elements 64 and a second die circumferentially split into a plurality of second die elements 66, to a more exactly true circle. Two cotters 68 and 70 are provided. Cotters 68 and 70 include tapered portions 72 and 74, respectively. As shown in FIG. 5, one cotter 68 is inserted into the first die and the other cotter 70 is inserted into the second die, and first and second die elements 64 and 66 are pushed radially outwardly by tapered portions 72 and 74 of first and second cotters 68 and 70 via circumferentially split segments 78 and 80, respectively. A left half portion of FIG. 6 illustrates an expansion state of die elements 64 and 66, while a right half portion of FIG. 6 illustrates a shrinkage state of die elements 64 and 66. When die elements 64 and 66 are radially outwardly pushed, rim element 62 is radially expanded and shaped. As shown in FIG. 7, when a split type die is used, the shaped rim element 62 will include a plurality of local, radially inwardly deformed portions 62p which are naturally formed due to clearances 76 between the die elements.
However, the prior art shaping apparatus has the following problems.
(a) Because the two cotters 68 and 70 are used and each cotter is constructed in the form of a cantilever, cotters 68 and 70 tend to be inclined and to come out of alignment with respect to each other when different transverse forces act on cotters 68 and 70. Such inclination and misalignment are illustrated in FIG. 8. The rim element which has been shaped under such inclination and misalignment of cotters 68 and 70 will be distorted as shown in FIG. 9. As a result, as shown in FIG. 10, when a disk 82 is inserted into the distorted rim element 62 at the successive disk insertion station, it will be difficult to smoothly insert disk 82 into rim element 62. Thus, a further distortion may happen in rim element 62 and disk 82, because an axis 84 of rim element 62 is inclined with respect to an axis 86 of disk 82.
(b) When such inclination and misalignment of cotters 68 and 70 happen, rim bead seat portions 62b and 62b located at the end portions of rim element 62 will be formed out of alignment with each other as shown in FIG. 11 which illustrates, in a developed state, the radial deflections A1' and A2' of the rim bead seat portions from a true circle. This causes a considerably severe transverse vibration of a vehicle when the disk wheel is mounted to the vehicle and is rotated.
(c) The local, radially inwardly deformed portions 62p formed in rim bead seat portions 62b of rim element 62 cause a vertical vibration of a vehicle when the disk wheel is mounted to the vehicle and is rotated. Further, radially inwardly deformed portions 62p formed in drop portion 62c of rim element 62 make it further difficult to insert disk 82 into rim element 62.